Method of welding



June 11, 1946. P, FHELD 2,402,031

METHOD OF WELDING Filgd April 3, 1940 N pauzl w.

Patented June 11, 1946 rm Fiield, mn nm, Mesa,- assign'or to BethlehemSteel Company, a corporation of Pennsylvania Application April 3, 1940,No. 327,602

This invention relates to an improved steel for turbine blading which isassembled by brazing the blades to the packing pieces and also for suchuses as sleeves for oil pumps and high pressure valves in which a hardwearing, surface is obtained by fusing Stellite overlays onto the steel;

in other words, where the-metal parts are united by a process involvingfusion, as by brazing, or welding. With the ordinary low carbon 12percent chromium stainless steel which is generally used for thesepurposes cracking of the brazed joints and of the Stelllte overlays isfrequently encountered.

We have discovered that this cracking is more apt to occur when thestainless steel goes through an expansion at a relatively lowtemperature on cooling after brazing or welding or after welding-on theStellite overlay. We observed that the frequency of cracking with steelin which an expansion takes place at a relatively high temperature oncooling, is much less than with steel in'which an expansion takes placeat a relatively low temperature. The explanation appears to be that boththe brazing alloy and the Stellite are more brittle at relatively lowertemperatures than at more elevated temperatures. The magnitude of theexpansion also tends to be considerably greater when it occurs at thelower temperature. Thus expansion of the steel (while the packing piecesto which the turbine blades are brazed are contracting or when theStellite overlay is contracting) at a, lower temperature frequentlycauses cracking of the brazed joint or Stellite overlay, but expansionat. a more elevated temperature does not.

Figure 1 shows dilatometer heating and cool-- ing curves of threedifferent steels. It will be observed that all. three steels go 'throughan expansion during cooling, but in steel A the expansion takes place atabout 600 F., in steel B P rtly at about 1400" F. and partly at about700 E, and in steel the expansion occurs at about 4 Claims. (01.113-412) v 2 g 1300 F. A faster rate of cooling tends to lower thetemperature at whichthe expansion occurs.

The rate of cooling in the dilatometer tests was purposely made ratherfast to simulate the rate 5 at which cooling takes place in a brazedjoint of turbine blading or in a welded overlay. In this way one is safei using the dilatometer test to ascertain whether the steel expands atan elevated temperature during cooling.

m The compofltions of the in Figure 1 are" given below:

0 Mn si Ni'Cr Me Al Percent Percent Percent Percent 0.54 12.48 0.44 None12. 28 None None 13 12,44 None .02

After an extended series of tests we found that when certain of theelements which may ordinarily occur in such steels as commerciallyproduced are present in more than minimal amounts, the temperature atwhich the expansion on cooling occurs is lowered. Thus thepresence ofmore than .35 percent manganese, more than .15 percent nickel, more than.15 percent copper, more than'.1 percent molybdenum, and

more than .1 percent carbon tended to lower the v expansion temperature.0n the other hand, in-

creasing the silicon content to about .4 percent tended to counteractthis. The addition of about .02 percent aluminum was particularlybeneficial in raising the expansion. temperature. Since sulphur combineswith manganese to form manganese sulphide, the eii'ect of increasing thesulphur content was to reduce the effect 01' manganese in lowering theexpansion temperature.

As a result of these tests the following compo- 40 sitlon was found tobe very suitable for turbine v blading assembledby brazing or'forsleeves for oil pumps and high pressure valves and other parts on whichStellite overlays are welded:

0 Mn Si Ni Cr Mo Cu Lu Percent Percent PM lercent Percent PercentPercent Percent 0. (5-0- 10 0. 15-0. 35 0. 40-0. 0- 15 1118!- 12.[IT-12. 50 None 0. 15 max. 0. (BED. 035

1350' 1-. Cracks in brazed joints and in Stellite overlays are much moreliableto occur in steel of types A and 3 than in steelof type C. The

rate of cooling in these dilatometer tests was about 7 F. perminute inthe neighborhood of 56 poses described above which have been tested byAlthough compositions such as those above will in general give anexpansion at a high tempera- .ture on cooling, still it is desirable toascertain this. Onh; such steels should be used for the purmanner thedilatometer test and actuall found to give an expansion at above 1300 F.

Having thus described my invention what I claim as new and desire tosecure by Letters Uniting the metal pieces by welding or brazing,

utillzing the chromium-bearing steel which has been ascertained to havean expansion above about 1300 F.

2. In a method of making turbine blading assembled by brazing orwelding, and containing up to about 0.1% carbon, about 11 to 15%chromium, and the balance mainly of iron, the steps of ascertaining theexpansion of the steel which take place on cooling as after brazing orwelding, and brazing or welding to produce the turbine blading utilizingthe steel whose expansion takes place on cooling above about 1300 F.

3. In a method of making articles on which overlays are welded, saidarticle containing up to about 0.1% carbon, about 11 to 15% chromium,and the balance mainly of iron, the steps of ascertaining the expansionwhich takes place on cooling as after the Welding operation, and Weldingthe overlays on the chromium steel Whose expansion on cooling after thewelding-on operation is above 1300" F.

4. in a method of making articles on which Stellite overlays are welded,said article containing up to about 0.1% carbon, about 11 to 15%chromium, and the balance mainly of iron, the steps of ascertaining theexpansion which takes place on cooling as after the Welding operation,and welding the overlays on the chromium steel Whose expansion oncooling after the weldingon operation is above 1300 F.

i PAUL

